Formula Sound FF-4.2L, User Manual

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The stereo balanced line input may be strapped for unbalanced operation.
Channel 1 has a compressor selected by a switch, the compressor operates on both
microphone and line inputs.
The compressor is factory set for a threshold of 0dB, a threshold LED between the
COMP and AUX 2 switch indicates when the compression threshold is reached.
The compressor is factory set for a soft compression when selected, the threshold and
compression ratio may be adjusted by controls that are recessed in the base of the unit
(see appendix 3).
The compression threshold can be adjusted by putting a piece of music that has an
even level through the channel and set the gain control so the channel meter indicates
the level you want to set the compressor threshold to. Adjust the compressor
threshold control until the threshold level LED just comes on, adjust back and forth a
few times to be sure you are at the right point.
Route the music to the output and set so the output meter indicates the same as the
input meter, check the compressor threshold LED is still on (increase the GAIN
setting if it is not until the LED comes on), then increase the GAIN setting by 6dB on
the channel meter and check the change in the output meter. The change in the output
meter should be less because it is compressed.
The amount of compression can be calculated, 1dB change on output meter is 6:1,
2dB change would be 3:1, 3dB change would be 2:1 and 4dB change would be 1.5:1
compression ratio. The ratio is change in input divided by change in output so if 6dB
change in input produces 3dB change in output the ratio is 6dB/3dB = 2 or 2:1.
Adjust the ratio control as required, if the output level is similar to the input level
there is little compression, if the output level is nearly 6dB less than the input then
there is approaching maximum compression. A 6dB change in input is used in this
example a larger or smaller change can be used.
The compressor should be selected before the audio is routed to the output, as there
may be a small audible click if the compressor is selected live.
The compressor is particularly useful for vocals and the high pass filter may be used
to remove some of the effects of breathing into a microphone by setting it to about a
quarter turn.
Channels 2 – 4
A stereo line input and a stereo phono input are the two inputs on channels 3 – 6
which are selectable on the input select switch. Both are on phono sockets.